This invention relates to direct current motor control devices for use in battery automobiles and more particularly to a direct current motor control device for use in battery automobiles which comprises a battery change-over thyristor circuit which is inclusive of a chopper circuit and which can control the voltage applied to the motor by means of the chopping operation of the chopping circuit and the series-parallel change-over operation of the battery groups.
In general, a driving motor for use in battery automobile is supplied with voltage from batteries through a chopper circuit. As the driving motor, a direct current series wound motor is often used due to its output characteristic and for ease of control. Sometimes, however, use may also be made of a shunt wound motor, compound wound motor or permanent magnet field motor.
The value of the average voltage applied to the motor through the chopper circuit is determined by the time ratio of the chopper circuit and by the battery voltage.
Let the time during which the chopper circuit is ON be Ton, the time during which the chopper circuit is OFF be Toff, the battery voltage be Eb and the total inductance of the series circuit be L, then the pulsating amplitude .DELTA.Im of the motor current is given by ##EQU1##
A large pulsating amplitude .DELTA.Im of the motor current results in difficult problems that the motor loss becomes increased, that commutating operation becomes worse to involve an abnormal wear of brushes, and that mechanical vibrations occur due to the torque pulsations. As a result, it is desirable to reduce the pulsating amplitude .DELTA.Im of the motor current as far as possible.
In order to reduce the pulsating amplitude, heretofore, it has been proposed (1) to increase ON and OFF repetition frequency (f = 1/Ton+Toff) of the chopper circuit and (2) to increase the inductance L in the series circuit. These measures, however, have been difficult in practice owing to a limitation subjected to the chopper circuit in its characteristic, weight and the like.